Via his Paradox Prism transformation. It's also implied this transformation allows Sonic to duplicate too, although not officially confirmed.
An immeasurable speed outlier is not evidence of infinite speed, and yes, it is an outlier because Wyvern scales not just to Super Sonic, but also downscales from an AMPED PEAK Super Sonic. No matter how consistantly base Sonic keeps up with the Titans, it will always be an outlier due to circular scaling. It's simply impossible for him to be even remotely comparable to his own current Starfall Super Sonic transformation.
That being said, I currently disagree with removing infinite speed for modern base forms not only because I think the current feats are valid, but because the ongoing cosmology revision will give us infinite sized universes, and therefore an infinite speed feat from Dodon Pa's rocket and Eggman's machines. On top of that there are in fact potential infinite speed feats in the Adventure era... I may bring them up if I have to.